How can I reorient objects to face surface normals on a sphere?

[magneto]

I am trying to do simple projects off top of my head to learn more about copy stamping, but this problem I am not sure how to solve inside Houdini.

Basically I am creating 1000 Grid SOPs on the surface of a Sphere using the Copy SOP, and it works fine. But I want the Grids to be oriented so they face away from the surface normals of the sphere, like its own polygons.

I am stuck because I don't know how to get the normals info from the sphere.

Here is the pic:

[3dbeing]

Make sure the normals exist first, right now it doesn't look like you sphere has normals. then make sure the grid is in the x/y plane, flat on the z. Basically what is pointing down positive z will be oriented pointing down the normal... create a cone (tube with one end radius = 0) to better understand how orientation works.. an up vector will also be be respected when using the copy sop...

[ben]

Up-vector seems to be the way.

look at this thread :

http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=10452&highlight=copy+align

[magneto]

Thanks guys, I did what you suggested and it worked. It's amazingly cool.

Btw now I have another problem. I know how to do it but couldn't find if houdini has something to help with this.

Basically I want to color these Grid SOPs so that they show the whole color spectrum say from bottom to top. I know I can do it with HSV very easily but the Color SOP is using RGB which wouldn't be possible to linearly interpolate colors. Also I could sort the points using the Sort SOP so it's no problem in the order but the color.

Any ideas on this?

Edited December 29, 2011 by magneto

[zarti]

id suggest fit() ;

so , in bottom to top case , fit ymin and ymax from 0 to 1 and assign that to the color channels .

or in general you can use a color ramp with BBY as a segment .

there might be other ways too .

--

im posting from a mobile so , sorry i couldnt post any file ..

[magneto]

Thanks zarti, but do ramps allow HSV assignment? Because otherwise I wouldn't be able to generate an HSV spectrum using RGB values.

Edited December 29, 2011 by magneto

[zarti]

afair , there is a Vop node which converts from hsv-rgb and viceversa .

so , there must be an Equivalent expression for that node too .

[magneto]

afair , there is a Vop node which converts from hsv-rgb and viceversa .

so , there must be an Equivalent expression for that node too .

Thanks man, I will check it out

[magneto]

I saw the VOP you are talking about but I don't know how to use it. I will try a different method as I am not familiar much with VEX stuff.

[kartik]

how to fix this aim direction??

aim_dir.hip

Edited June 24, 2018 by kartik

[kartik]

fixed

 

aim_dir_fixed.hip

 

pop vop velocity is pointed to normal 

 

Thanks

 

bees_v002.hip

Edited June 24, 2018 by kartik